In the course of study of drug metabolism and the like it is often necessary to collect fractions from a liquid chromatographic column for further analysis by such methods, for metabolites for example, as high resolution mass spectrometry. Less frequently, but nevertheless important, large scale liquid column chromatography is used for purification of drugs synthesized in the laboratory. In many cases the chromatograph peaks corresponding to the fractions which it is desired to collect are not sufficiently separated so that a conventional timed collection of fractions is satisfactory. Resort must be had to fraction collectors which can be made to collect "peaks" when they are connected to a peak detecting device. Many such collectors are available but are generally expensive and because they are electronic in nature are highly susceptible to error due to electrical noise and irregularities in the base-line. Corrections for such errors are both difficult and time consuming.